lec 5-Gene Interaction I: Types of Mutation and Departure from Mendelian Ratios

Vocabulary flashcards detailing mutation types (amorphic, hypomorphic, etc.), dominance variations, lethal alleles, and non-Mendelian inheritance patterns including X-linkage and maternal inheritance.

Amorphic (null) mutation

A loss of function mutation that produces no protein at all, or a protein product that completely lacks function; usually recessive.

$$CFTRΔ508$$

An amorphic recessive allele that does not exit the endoplasmic reticulum, leading to cystic fibrosis due to the loss of the $Cl^-$ gradient.

Hypomorphic (leaky) mutation

A loss of function mutation where protein function is reduced because less protein is made or the product itself displays less activity; usually recessive.

Hypermorphic mutation

A gain of function mutation resulting in an increase in activity, either by making more protein or creating a protein with greater activity; usually dominant.

Antimorphic (dominant negative) mutation

A gain of function mutation where the mutant protein interferes with the function of the normal allele product, often in hetero- or homo-multimers.

Dominant lethal allele

A rare gain of function mutation where the onset of disease is caused by the accumulation of mutant product, requiring the affected individual to reproduce before death to persist in a population.

Huntington’s disease

A dominant lethal condition caused by a triplet expansion of >36 CAG repeats in the HD locus, leading to neurotoxic protein aggregation.

Neomorphic mutation

A gain of function mutation that alters the protein function to a 'new form', such as the Antennapedia mutation in Drosophila where legs grow instead of eyes.

Incomplete (partial) dominance

A pattern of inheritance where the heterozygote displays a 'blend' of characteristics, resulting in a $1:2:1$ phenotypic ratio for red, pink, and white blossoms in four o’clock plants.

Co-dominance

A pattern of inheritance where the presence of both alleles is detected equally, such as the $I^A I^B$ genotype resulting in blood type AB.

Lethal allele

An allele that distorts Mendelian ratios by causing death in utero for certain genotypes, such as the $A^y A^y$ yellow mouse genotype which results in a $2:1$ ratio of yellow to wild type offspring.

Genetic load

The collection of lethal alleles present within a population.

X-linkage

A pattern of inheritance for genes on the X chromosome where males inherit their X from the mother, often meaning they are more frequently affected by recessive traits.

Sex-limited trait

A trait encoded by autosomal genes but where the phenotype is absolutely restricted to one sex, such as milk yield in dairy cattle.

Sex-influenced trait

A trait where the phenotype's expression depends on hormone constitution, such as male pattern baldness which acts as a dominant trait in males and recessive in females.

$2 ext{D}:4 ext{D}$ ratio

A sex-influenced ratio of the 2nd to 4th digit length, where the 2nd digit is typically shorter in males and longer in females.

Maternal inheritance

The exclusive inheritance of mitochondrial and chloroplast DNA from the mother, meaning mitochondria from sperm or pollen are excluded from the zygote.

Incomplete penetrance

When the phenotype associated with a specific genotype fails to appear in some individuals, such as only 25-30 ext{%} of polydactyly carriers developing extra digits.

Variable expressivity

A situation where a phenotype varies in the degree of magnitude or specific features expressed among individuals with the same genotype.

Pleiotropic

A term describing an allele that affects more than one character, such as those found in Wardenburg syndrome.